1. Field of the Invention
The present invention relates to a non-contact type tonometer for measuring intraocular pressure by compressing fluid in a cylinder, blowing compressed fluid against an examined eye, and detecting a deformed state in the cornea of the examined eye.
2. Description of the Related Art
As a non-contact type tonometer, there is known one of a mechanism in which air in a cylinder is compressed by a piston and compressed air is blown against an examined eye through a nozzle from a compression chamber for conductively connecting to the cylinder to deform the cornea. For the intraocular pressure of the examined eye, a deformed state in the cornea caused by blowing compressed air is detected, and air pressure when the cornea has been deformed into a predetermined state is directly or indirectly detected to thereby measure on the basis of the air pressure thus detected at that time. The air to be blown against the examined eye is compressed by supplying current to a driving device such as a solenoid to drive the piston. After the detection of the deformed state of the cornea, energizing of the piston driving device is stopped to return the piston to the initial position by a restoring force such as a spring. At this time, air is sucked in through the nozzle.
In a process of sucking in outside air through the nozzle by such return of the piston, however, when the piston is suddenly returned, tears, dust, eyelashes and the like are prone to be sucked in the cylinder through the nozzle. The tears, dust, eyelashes and the like thus sucked contaminate the optical system arranged behind the nozzle, and eyelashes and the like may enter a gap between cylinder and piston to lock the piston. Further, since the dust and the like which have been sucked are blown against the examined eye again, it is not desirable also in view of hygiene.
In the light of the above-described problems, it is a technical problem of the present invention to provide a non-contact type tonometer capable of restraining tears, dust, eyelashes and the like from being sucked in through the nozzle as effectively as possible with a simple structure.